The present invention relates generally to methods and systems for operating a camless internal combustion engine. More particularly, the invention relates to methods and systems for using pulsed intake valve operation to adjust for transient engine loads.
Camless internal combustion engines are known in the art and are used primarily to provide variability in valve timing, duration and lift. Valves in camless engines are typically actuated using electromechanical or electrohydraulic actuators, and as such can be actuated accordingly to achieve optimal or desired engine performance. A typical electromechanical actuator uses one or more solenoids to generate a magnetic field to attract and displace an armature, which in turn actuates one or more corresponding valves, whereas a typical electrohydraulic actuator utilizes fluid pressure controlled by one or more solenoids to operate corresponding valves. The opening and closing times of the valves are typically controlled as a function of one or more engine parameters such as speed, demanded engine torque and crankshaft angular position.
Internal combustion engines, both camless and cam-based, are often susceptible to sudden transient load demands, e.g., traction control events, transmission shifts, sudden changes in driver demand, etc., which may be considered to achieve desired engine performance. Although conventional spark retard techniques have been used to compensate for sudden load changes, such techniques remain undesirable due to inefficient burning of the air-fuel mixture and heating of corresponding exhaust system components.
As such, the inventors have recognized that camless engines provide an opportunity to respond to rapid changes in demanded load without using conventional spark retard techniques. Such an opportunity exists, for example, when there is a need to respond to a rapid load change occurring during the present engine cycle after a commanded amount of fuel and air charge has already been provided to one or more combustion chambers of an internal combustion engine.
The aforedescribed limitations and inadequacies of conventional control methods are substantially overcome by the present invention, in which a method is provided for controlling valve actuation in an internal combustion engine. The method, which can be used to operate direct fuel injection (DFI), port fuel injection (PFI) and diesel internal combustion engines, includes the steps of providing quantities of air charge and fuel required to produce a commanded air-fuel mixture within a combustion chamber of the internal combustion engine, and displacing a quantity of the air-fuel mixture from the combustion chamber in response to the transient load. A combustion event is then performed to burn the air-fuel mixture remaining within the combustion chamber.
An advantage of the present invention is that changes in commanded loads occurring after a commanded air-fuel mixture has been provided to the combustion chamber can be adjusted during the present engine cycle to compensate for sudden changes in load demand. Sudden changes in load demand can result, for example, from sudden or unexpected traction control, transmission shift and driver demand events. In addition, the disclosed method avoids the disadvantages of conventional spark retard techniques such as reduced air/fuel burn efficiency and overheating of a corresponding exhaust system.
In accordance with another preferred method, the intake and exhaust valves of the internal combustion engine are closed accordingly to introduce an amount of air charge required to produce a commanded air-fuel mixture within the combustion chamber. An amount of fuel is also provided, either before or after the air charge is provided, to produce the commanded air-fuel mixture. In response to a transient load, the intake valves are then reopened and reclosed during a subsequent compression stroke of the engine to displace a portion of the air-fuel mixture and thus adjust the volume of the air-fuel mixture within the combustion chamber. Optionally, the method further includes the step of adjusting the commanded air-fuel mixture -for a subsequent engine cycle to compensate for the displaced amount of air-fuel mixture.
Alternatively, in lieu of reopening and reclosing the intake valve, another preferred method of the present invention includes the step of delaying a combustion event for the engine cycle by n number of engine revolutions. Delaying or xe2x80x9cskippingxe2x80x9d a corresponding combustion event for one or more engine revolutions thereby compensates for the transient load.
In accordance with another aspect of the present invention, a corresponding valve control system is provided for operating a camless internal combustion engine in response to a transient load. The system includes at least one sensor from which the transient load is computed, an electronic actuator coupled to the at least one intake valve, and an engine controller coupled to the at least one sensor, the electronic actuator and the at least one fuel injector. Advantageously, the engine controller is adapted for controlling the supply of fuel and air charge quantities required to produce a commanded air-fuel mixture within the combustion chamber, and for controlling the displacement of a portion of the air-fuel mixture from the combustion chamber in response to the transient load.
Still further, in accordance with yet another aspect of the present invention, an article of manufacture is provided for operating a camless internal combustion engine in response to a transient load, wherein the internal combustion engine is characterized by a predefined engine cycle and a plurality of cylinders each having a corresponding combustion chamber, each cylinder having at least one exhaust valve, at least one intake valve and at least one fuel injector for providing fuel to the combustion chamber. The article of manufacture includes a computer usable medium and a computer readable program code embodied in the computer usable medium for directing the computer to perform the steps of controlling the operation of the at least one exhaust valve, the at least one electronically-actuated intake valve and the at least one fuel injector. The program code further directs the computer to control the supply of fuel and air charge quantities required to produce a commanded air-fuel mixture within the combustion chamber, and to control the displacement of a portion of the air-fuel mixture from the combustion chamber in response to the transient load.
Alternatively, a system and an article of manufacture are provided having an engine controller and computer program code, respectively, for delaying a corresponding combustion event by one or more engine revolutions.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.